The present invention relates to a hydraulic machine comprising several pistons sliding in cylinders, a method for calculating the openings of the manifolds of this machine, and a hybrid vehicle equipped with such a hydraulic machine.
A known type of hydraulic machine with a drum, presented in particular in U.S. Pat. No. 5,358,388, comprises a motor driven input shaft which rotationally drives a drum barrel having a succession of parallel cylinders regularly distributed around the axis of the shaft. Each cylinder receives a piston which rests axially on one side, called by convention the front side, on a tilting tray which is fixed in rotation, through the intermediary of a bearing forming an axial abutment.
One rotation of the drum moves each piston according to a complete cycle with a stroke which depends on the tilt angle of the tray, the angle being adjustable by a tilt command. In this way, the displacement can change from zero when the tilting tray is perpendicular to the shaft, to a maximum displacement when the tilt of the tray is at its maximum.
The rear face of the drum, opposite the tilting tray, rests against a fixed circular plate which closes the ends of the cylinders, in order to ensure sealing. The plate comprises a low pressure manifold and a high pressure manifold each forming a circular arc located facing a series of cylinders, the manifolds being separated by sufficient space so that each of the cylinders closes one of the manifolds before opening the other.
With these piston machines, each time a cylinder opens to one of the manifolds, a pressure shock is generated in the cylinder which reverberates via the piston to the tilting tray, producing vibrations of the machines resulting in noise emissions. The noise emissions have a main frequency corresponding with the number of cylinders multiplied by the rotational speed of the machine, and multiple harmonic frequencies of this main frequency, which generate a noise similar to that of a siren.
To limit the noise emissions, certain openings of the ends of the cylinders, resting against the plate, comprise relative to their cylinders, a small angular offset tangent to the direction of rotation, which is limited to a few degrees. In particular, certain openings are aligned on the cylinder, without offset, while others are, according to the direction of rotation of the drum, a little in advance or behind relative to their cylinders.
In this way, inside a total offset adjustment range centered on the axis of the cylinder, there are different degrees of offsets, comprising a null offset, small offsets on both sides, and large offset on both sides.
The above-mentioned prior art document provides, for this type of hydraulic machine, a reduction of certain frequencies of noise emissions, due to the relative irregularity of the successive periods between the openings and the closings of each cylinder relative to the collectors.
However, tests have shown that the reduction of noise emissions is not sufficient, in particular for applications in a hybrid vehicle comprising pumps and hydraulic machines rotating at relatively high speeds, in order to store hydraulic energy in one of the pressure accumulators and to return the pressure afterwards to save energy.
In addition, in these vehicles the noise signature emitted by this type of machine has the effect of a siren, which is very different from the noise emissions of the combustion engine. These noises are unpleasant, and can bother the driver and those with the driver, in particular when driving in hybrid mode which occurs alternatively and automatically, by switching from combustion engine traction to hydraulic motor traction.